The present invention relates to a direct encoding system for composite video signal, in particular, relates to such a system which uses Hadmard conversion and inter-frame motion compensation for high quality transmission of video signal.
Conventionally, composite video signal including luminance signal and chrominance signal is converted to component video signal which has separated luminance signal and chrominance signal so that each component signals (luminance signal and chrominance signal) are separately compressed and reproduced. Then, those component signals are combined to composite signal in a reproducing side.
FIG. 9 shows a block diagram of a conventional converter between composite video signal and component video signal.
FIG. 9A shows the case that composite video signal is converted to component video signal. In FIG. 9A, the numeral 100 is an input terminal of composite video signal E.sub.M which includes both luminance signal E.sub.Y and chrominance signal. The numeral 102 is a hybrid circuit for separating luminance signal E.sub.Y and chrominance signals (E.sub.R-Y, E.sub.B-Y). The separated luminance signal E.sub.Y is output to the output terminal 120. The chrominance signals are applied to the modulators 104 and 106 which modulates the chrominance signals with the sub-carrier signals cos(2 f.sub.sc +.phi.) and sin(2 f.sub.sc +.phi.) where f.sub.sc is color sub-carrier frequency and is equal to 3.58 MHz. The first chrominance signal (E.sub.R-Y) thus modulated is applied to the output terminal 122 through the low pass filter 108, the multiplier 112 which multiplies the constant b.sub.1 =2.28 and the 2:1 sub-sampling circuit 116. Similarly, the second chrominance signal (E.sub.B-Y) is applied to the output terminal 124 through the low pass filter 110, the multiplier 114 which multiplies the constant b.sub.2 =4.06 and the 2:1 sub-sampling circuit 118.
FIG. 9B shows a converter from component video signal to composite video signal. The component signals E.sub.Y, E.sub.R-Y and E.sub.B-Y are applied to the input terminals 130, 132 and 134, respectively. The luminance signal E.sub.Y is applied to the adder 152. The chrominance signals are applied to the 1:2 up-sampling circuits 136 and 138, respectively. The first chrominance signal is applied to the demodulator 148 through the multiplier 140 which multiplies the constant a.sub.1 =1/1.14, and the low pass filter 144. The second chrominance signal is applied to the demodulator 150 through the multiplier 142 which multiplies the constant a.sub.2 =1/2.03 and the low pass filter 146. The demodulators 148 and 150 which are supplied with the color sub-carrier signals cos(2 f.sub.sc +.phi.), and sin(2 f.sub.sc +.phi.), respectively, demodulate the chrominance signals, and provide the outputs to the adder 152, which provide the composite video signal E.sub.M to the output terminal 154.
If composite video signal is directly encoded without converting it to component signals, a direct encoding system has the advantages that an encoding system is simple in structure, and no signal deterioration due to decrease of resolving power because of the use of filters, leakage between luminance signal and chrominance signal, and the round error in sampling process occurs.
Therefore, a direct encoding system which encodes a composite video signal directly is preferable for high picture quality transmission.
However, conventional information compression system takes inter-frame motion compensated DCT (discrete cosine transform) system which handles component signal with prediction encoding system because of high compression ratio.
When a composite video signal is separated or converted to component video signal, some filters are used for separating luminance signal and chrominance signal, and therefore, deterioration of picture quality is unavoidable.
Therefore, if we try to use component video signal, deterioration of picture quality because of composite to component conversion process is unavoidable. Further, although inter-frame encoding system is useful for high compression ratio, it is not useful for composite video signal, since composite video signal has chrominance signal modulated with sub-carrier signal multiplexed with luminance signal, and therefore, even if a composite video signal is encoded through inter-frame encoding system on time region axis, high compression ratio is not obtained because of phase error of sub-carrier signal.